1c) The benefit that virtue increases ever higher

As for this virtue corresponding with merit:

Other kinds of happiness diminish and are exhausted.
The happiness that is established by precious bodhicitta,
Rather than being exhausted, will actually increase.
It is like clear water flowing into the ocean,
Or an abundant harvest, growing in fertile soil.

A drop of water flowing into an ocean will not be exhausted even after a kalpa, but instead will increase. A sesame seed planted in good soil will greatly increase itself. So it is with the goodness accomplished by arousing bodhicitta. The Sutra Requested by Maitreya says:

Maitreya, for example, it is like this, however much water flows from great oceans full of water, even in a kalpa they will not be exhausted. Mañjushri, similarly the virtue accomplished by arousing bodhicitta will not be exhausted until attaining the unsurpassable enlightenment of buddhahood.

Maitreya, for example it is like this, all seeds which are a good source in every way will grow. As those seeds will grow, the goodness of having aroused bodhicitta will also vastly grow.

Meritorious goodness is not like a banana tree, which fruits once, and then is exhausted. The immeasurable fruition of temporal and ultimate goodness increases inexhaustibly like the fruiting of a great tree. The Bodhicharyavatara says:

All other kinds of virtue are like a banana tree
Having once brought forth fruit, then it is exhausted.
However the eternal tree of bodhicitta
Gives fruit that always increases inexhaustibly.

The Sutra Designed as a Jewel Chest (ratnakaranda sutra, za ma tog bkod pa'i mdo) says:

Mañjushri, it is like this, a variety of trees, having taken in the four elements, will greatly
increase. Mañjushri, if virtuous roots, having taken in bodhicitta, are dedicated to omniscience, they too will greatly increase.